Thermocell battery



March 28, 1967 SENDEROFF THERMOCELL BATTERY Original Filed March 9, 1961 5 HEAT EXCHANGER Cl 900C.

NUCLEAR REACTOR HEAT EXCHANGER ELECTROLYTE NONCONDUCTING CASE MANIFOLD 3 INVENTOR.

SEYMOUR SENDEROFF ATTONEV k United States Patent 9 Claims. (Cl. 13686) This application is a divisional application of United States Ser. No. 94,619, filed Mar. 9, 1961.

This invention relates to a thermocell with gas electrodes and molten salt electrolyte which may be used for direct conversion of heat to electricity and consists of two identical electrodes in contact with an electrolyte. A thermocell is equivalent to a thermocouple with one of the electronic conductors replaced by an ionically conducting electrolyte.

When a temperature diflference is maintained between the electrodes, an electrical potential difference will be developed between them. If a closed external circuit is provided between them, current will flow through the cell. As a result of the electrochemical processes at each electrode, material is transferred from one electrode to the other when the current flows.

Several thermocell systems already have been suggested and tried in the prior art. One such system, which may be called type (a) consists of solid electrodes with a liquid or solid electrolyte.

Systems of type (a) are inconvenient because the electrode material removed from the hot side deposits in a poor physical form on the cold side and is not amenable to reuse by reversing the cell with respect to the temperature gradient. Furthermore, the reversal itself is inconvenient. Liquid electrodes in cells of type (a) are undesirable for many reasons, and particularly because of the low thermoelectric power (10* to 10* millivolts per degree centigrade) they exhibit.

Another thermocell system, type (b), consists of two gas electrodes with a solid electrolyte.

Systems of type (b) can operate only at temperatures below the melting point of the electrolyte. Further, solids having sufficiently high electrical conductivity, all of it ionic, are not presently available at temperatures above 500 C.

Viewed against the background of the above-outlined prior art, an object of the present invention is to provide an improved gaseous thermocell, free from the limitations of prior art devices of this class.

A further object of this invention is to provide an improved thermocell capable of operating at high current densities with little polarization.

Another object of this invention is to provide an improved therrnocell capable of operating with a very large temperature gradient which is not easily accomplished with aqueous systems.

Another object of this invention is to provide a thermocell capable of operating efficiently at very high temperatures near 1000 C. and higher.

An additional object of the present invention is to provide a gaseous thermocell capable of using a wide variety of heat sources for its operation.

These and other related objects, features and advantages of the present invention will be more readily understood as the description thereof proceeds; particularly when taken together with the accompanying drawing, wherein:

FIGURE 1 is a schematic representation of a system using the present cells.

FIGURE 2 is a detailed, front elevational view of cells stacked in accord with the invention.

Broadly defined, the gaseous thermocell of the present invention comprises electrodes consisting of a gas in contact with a molten salt electrolyte containing simple or complex ions of the gas, and inert current collectors on which the electrochemical reaction involving the gas, electrolyte, and liberated or absorbed electrons occurs. The cell may have chlorine in contact with pure or mixed molten chloride electrolytes; or oxygen in contact with pure or mixed molten oxide electrolytes; or salts with oxygenated anions or cations; or, of hydrogen gas in contact with molten hydroxides, hydrides or acid salts, together with porous current collectors composed of carbon, graphite, transition metals and oxides thereof, or tantalum, silver or platinum. With respect to these collectors, it should be noted that selection of a particular material for the collector depends on the particular gas used in the system and on the composition of the electrolyte. Generally, however, graphite may be used with chlorine and hydrogen. The other listed materials are more suitable for use in conjunction with oxygen gas. Whatever the material, the collectors on the hot and cold side of the cell are identical.

The electrolyte employed in any given thermocell constructed in accord with the teachings of this invention should have the following properties:

(1) Low melting point.

(2) High boiling point.

(3) Low vapor pressure.

(4) High electrical, conductivity of an exclusively ionic nature.

(5) Low thermal conductivity.

(6) It must be capable of rapid reaction with the gas electrode.

Referring now to the drawing, FIGURE 1 shows schematically a system which employs the present cell. The cell is represented in its simplest form and denoted generally by reference character 1. In this form, the cell consists simply of two inert, porous, current collectors 2 and 3, having suitable channels for transporting gas in their outer faces for bringing gas to the collectorelectrolyte interface and having a layer of molten salt electrolyte 4 sandwiched between their inner faces. Conduit means 6 shown in FIGURE 2 and by the arrow in FIGURE 1 bring hot chlorine gas (at for example 900 C.) to the manifold associated with hot current collector 3 from a heat exchanger through one part of which circulates reactor coolant from a nuclear reactor. Another conduit denoted by arrow 5 takes the chlorine, which has lost some of its heat as a result of heating collector 3, to a second heat exchanger. Here, the chlorine gas loses more heat to reach a temperature of say 500 C. and is conveyed to cold collector 2 through conduit 8. Another conduit 12 takes the chlorine from collector 2 and on to the second and finally to the first heat exchanger for recirculation through the cell. A pump, inserted preferably at a position near arrow 5 (downstream from the hot collector), circulates the gas through the collectors and heat exchangers. This pump also assists in drawing into the stream the gas produced at the inner-face of collector 2 and in forcing through collector 3 the gas consumed at its inner-face.

It will be apreciated, however, that any suitable heat source may be used instead of the one shown.

With a battery constructed as above-described and using chlorine gas at 900 C. and 500 C., silver chloride as the electrolyte and porous graphite as collectors, a thermoelectric power of 0.65 millivolt per degree centigrade was obtained. 0.55 millivolt per degree centigrade was the thermoelectric power obtained when silver chloride was replaced by the eutectic mixture of potassium chloride-lithium chloride containing 54.5 weight percent of potassium chloride. The observed current densities were as high as 700 milliamperes per centimeter square with very little polarization. It should be noted from these two examples that the thermoelectric power of the subject cell when a chlorine electrode is used in conjunction with a chloride melt, varies only slightly with a change in cation when the cation is a simple chloride ion. 7 With complex chloride ions in the electrolyte, i.e. (AlCh) in NaAlCl, electrolytes, larger thermoelectric powers are obtained of the order of about 1.0 to 1.4 mv. per degree centigrade.

The sandwich of FIGURE 1 may be repeated, interpo'sing between each unit a layer of molten salt electrolyte, the assembly being stacked either vertically as shown (in FIGURE 2 or horizontally. The gas channels of alternate collectors (i.e., the hot collectors 3) are connected to an intake and exhaust manifold, as are the gas channels in the other set of alternate collectors (is. the cold collectors 2). The desired temperatures in the alternate sets are maintainedby means of the heat exchangers, and the how rate by means of the pump of the circulating gas. Electrical leads 20, 22 connected to the end collectors, one hot and one cold, take off the current generated by the battery. Where the gas mainfolds are good electrical conductors as in the case of graphite, this results in a parallel cell arrangement. A number of such batteries may be externally connected in series or parallel. Desired combinations of series and parallel cell arrangements may thus be made. The entire battery is enclosed in a non-conductive container 10, the material determined by the nature of the electrolyte and operating temperatures; i.e., fused silica or alumina for molten chlorides, fused magnesia for molten carbonates.

Alternatively, the assembly of FIGURE 1 may be enclosed in a suitable ceramic frame, with the collectors cemented into the frame. Such units may be stacked horizontally, each separated from its neighbor and series connected by joining the cold collector of one cell to the hot collector of the next with a good electrical conductor, preferably composed of the material of the collector itself.

What is claimed is:

1. A thermocell battery comprising a non-conductive container and in said container a plurality of unit cells each comprising a first porous carbon collector adapted to receive a gas at a given temperature and to release said gas at a lower temperature and a second porous carbon collector adapted to receive the same gas at a higher temperature than that received by said first collector, and adapted to release said gas at a lower temperature; a molten electrolyte containing ions of said gas intermediate said first and second collectors, gas conduits for bringing to and removing gas from said collectors, said conduits communicating with each other,

means for maintaining said gas at said given temperature and said higher temperature, respectively, and electrically conducting means connecting the first collector of one unit cell to the second collector of the next cell.

2. The battery of claim 1, wherein said unit cells are stacked horizontally.

3. The battery of claim 1, wherein said unit cells are stacked vertically.

4. A thermocell battery comprising a non-conductive container and in said container a plurality of unit cells, each comprising a first porous collector adapted to receive hydrogen gas at a given temperature and to release said gas at a lower temperature; a second porous collector adapted to receive hydrogen gas at a higher temperature than that received by said first collector and adapted to release said gas at a lower temperature; a molten electrolyte selected from the group consisting of hydroxides, hydrides and acid salts, said electrolyte lying intermediate said first and second collectors, said conduit means communicating with each other; means for maintaining the gas at said given temperature and said higher temperature, respectively; conduit means for bringing the gas to and removing the gas from said collectors; and electrically conducting means connecting the successive collectors of said units.

5. The battery of claim 4, wherein said container is a ceramic frame and said collectors are cemented into said frame, with the first collector of one cell electrically connected to the second collector of'the next cell.

6. A thermocell battery comprising a non-conductive container and in said container a plurality of unit cells, each comprising a first porous collector adapted to receive oxygen gas at a given temperature and to release said gas at a lower temperature; a second porous collector adapted to receive oxygen gas at a higher temperature than that at which the gas is received by said first collector, and adapted to release said gas at a lower temperature; a molten oxidic electrolyte intermediate said first and second collectors; conduit means for bringing the gas to and removing the gas from said collectors, said conduit means communicating with each other; means for maintaining the gas at said given temperature and said higher temperature, respectively; and electrically conducting means connecting the successive collectors of said units.

7. The battery of claim 6 wherein said container is a ceramic frame and said collectors are cemented into said frame, with the first collector of one cell electrically connected to the second collector of the next cell.

8. A thermocell battery comprising a non-conductive container and in said container a plurality of unit cells, each comprising a first porous collector adapted to receive chlorine gas at a given temperature and to release said gas at a lower temperature; a second porous collector adapted to receive chlorine gas at a higher temperature than that at which the gas is received by said first collector and adapted to release said gas at a lower temperature; a molten chloride-containing electrolyte intermediate said first and second collectors; conduit means for bringing the gas to and removing the gas from said collectors, said conduit means communicating witheach other; means for maintaining the gas at said given temperature and said higher temperature, respectively; and electrically conducting means connecting the successive collectors of said units.

9. The battery of claim 8 wherein said container is a ceramic frame and said collectors are cemented into said frame, with the first collector of one cell electrically connected to the second collector of the next cell.

References Cited by the Examiner UNITED STATES PATENTS 4/1953 Bichowsky 13686 4/1959 Liebhafsky l3686 X UNITED STATES PATENT OEFIC'E CERTIFICATE OF CORRECTION Patent No. 3,311,506 March 28, 1967 Seymour Senderoff It is hereby certified that error appears in the above nmnbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 7, beginning with "collectors, said" strike out all to and including "said collectors" in line 11, same column 4, and insert instead collectors; conduit means for bringing the gas to and removing the gas from said collectors, said conduit means communicating with each other; means for maintaining the gas at said given temperature and said higher temperature, respectively Signed and sealed this 14th day of November 1967.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents EDWARD M.FLETCHER,JR. Attesting Officer 

4. A THERMOCELL BATTERY COMPRISING A NON-CONDUCTIVE CONTAINER AND IN SAID CONTAINER A PLURALITY OF UNIT CELLS, EACH COMPRISING A FIRST POROUS COLLECTOR ADAPTED TO RECEIVE HYDROGEN GAS AT A GIVEN TEMPERATURE AND TO RELEASE SAID GAS AT A LOWER TEMPERATURE; A SECOND POROUS COLLECTOR ADAPTED TO RECEIVE HYDROGEN GAS AT A HIGHER TEMPERATURE THAN THAT RECEIVED BY SAID FIRST COLLECTOR AND ADAPTED TO RELEASE SAID GAS AT A LOWER TEMPERATURE; A MOLTEN ELECTROLYTE SELECTED FROM THE GROUP CONSISTING OF HYDROXIDES, HYDRIDES AND ACID SALTS, SAID ELECTROLYTE LYING INTERMEDIATE SAID FIRST AND SECOND COLLECTORS, SAID CONDUIT MEANS COMMUNICATING WITH EACH OTHER; MEANS FOR MAINTAINING THE GAS AT SAID GIVEN TEMPERATURE AND SAID HIGHER TEMPERATURE, RESPECTIVELY; CONDUIT MEANS FOR BRINGING THE GAS TO AND REMOVING THE GAS FROM SAID COLLECTORS; AND ELECTRICALLY CONDUCTING MEANS CONNECTING THE SUCCESSIVE COLLECTORS OF SAID UNITS. 